He was rushed to Northern Westchester Hospital, where he was later pronounced dead.
Police say the boy could have been in the water for as long as 14 minutes.
"We found the body of a boy floating in the water, pulled him out, attempted to revive him and loaded him on an ambulence," Chief David Ryan said.
Town police officers, state police troopers and emergency medical technicians were at the scene near the Lewisboro border.
It is not clear if the child lived nearby or was visiting relatives.
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